Syria has accused a young woman blogger of spying for a foreign power after human rights watchdogs raised her case as an example of unjustified restrictions on freedom of expression.

The Associated Press today quoted an unnamed official in Damascus as confirming media reports that Tal al-Mallouhi, 19, was being held for alleged involvement in espionage for a foreign country.

"Her spying led to an attack against a Syrian army officer by the agents of this foreign country," the official said. This was believed to be the first government comment on the case. Supporters of the blogger are unlikely to believe it.

Mallouhi, a student from Homs, was summoned for interrogation last December and immediately detained. Her computer, CDs, books and other belongings were confiscated. Her blog was known for its poetry, social commentary and passionate focus on Palestinian issues. Its home page shows a picture of Gandhi and a poem in praise of Jerusalem.

The New York-based watchdog Human Rights Watch raised the profile of Mallouhi's case last month when it described her detention as "typical of the cruel, arbitrary behaviour of Syria's security services".

President Bashar al-Assad's government is sensitive to foreign criticism of its human rights record. Amnesty International has also appealed for her immediate release.

Syrian activists have expressed concern that the teenager may have been detained because of a poem she wrote criticising restrictions on the freedom of expression. Her family reportedly did not initially publicise her arrest because they were hoping to obtain her release through discreet negotiations with the authorities.

Syrian media reported that her parents had visited her in Douma women's prison near Damascus last week – the first time they had seen her since her arrest. But supporters have treated with scepticism her father's claim that she was not in trouble because of her blog but for reasons of "national security". Protest vigils were held over the weekend in several European capitals as well, as in Cairo, in Egypt, Lahore, in Pakistan, and Sana'a in Yemen.

Campaigners have used Facebook to mobilise support, and the BBC's popular Arabic service has canvassed opinions about her plight.

Critics of the Assad regime say Syria now has both the oldest and youngest prisoners of conscience in the Arab world: Haitham al-Maleh is 80-years-old; at 19, al-Mallouhi is said to be the youngest.

Amnesty has reported that Mallouhi is frail and suffers from an abnormally accelerated heart rate (tachycardia), and that there are concerns for her health. It said last month it has documented 38 different types of torture and ill-treatment used against detainees in Syria.